The present invention relates to a gas turbine combined power generation system, and more particularly, to a direct coal fired type gas turbine combined power generation system utilizing a pressurized gasifier provided with a gas refining equipment and a dust collecting equipment capable of preventing from lowering the thermal efficiency of the power generation system which is resulted through cooling a scrubbed raw gas for the utilization for the gas refining equipment.
FIG. 2 is a conventional system diagram showing a coal gas combined power generation system utilizing a pressurized entrained flow coal gasifier disclosed, for example, in the Japanese Patent Publication (KOKOKU) No. 44882/1989. In the illustrated conventional power generation system, a coal 101 is gasified in a gasifier 103 utilizing air or oxygen as an oxidant 102 and then exhausted as a raw gas 104 of high pressure and high temperature. The thus exhausted raw gas 104a enters a high temperature scrubber 105 in which unburned carbon content and an ash content are removed. The scrubbed raw gas 104b then enters a steam generation unit 106 to carry out a heat exchanging operation to reduce its temperature and further enters a gas/gas heat exchanger 107 in which a heat exchanging operation is performed between the scrubbed raw gas 104b and a clean gas 108. Through this operation, the scrubbed raw gas 104b is lowered in its temperature to a temperature required for a gas refining unit 109, in which the gas is refined for the purposes of corrosion prevention to the gas turbine and safeness of environment.
The clean gas 108 is heat-exchanged in the gas/gas heat exchanger 107 with the scrubbed raw gas 104b, thus increasing its temperature, the gas is fed to a gas turbine combustor 111 as a fuel gas 110 and then burned therein. The exhaust gas in high temperature state is transferred to a gas turbine 112 to perform its working, and then, in a gas turbine generator 113, is converted into an electric energy. Thereafter, the gas is exhausted as a gas turbine exhaust gas 114, in which a sensible heat is recovered in heat recovery boiler 115 to generate steam. Thereafter, the gas 114 is released in an atmosphere.
The prior art described above can provide a combined power generation plant with high thermal efficiency having a structure capable of reacting the coal and the oxidant in the gasifier, producing and refining a fuel by reducing a temperature of the generated gas, driving the gas turbine by a high temperature gas generated by the burning of the fuel gas, recovering the sensitive heat in the gasifier, the steam generator and the heat recovery boiler to thereby generate steam and driving the steam turbine to perform the power generation.
However, in such prior art, when the gas exhausted from the gasifier is fed to the gas turbine, there is utilized a system in which the once produced gas is cooled to a temperature required for the gas refining unit, then increased in its temperature by means of the gas/gas heat exchanger and further burned to feed the gas into the gas turbine for the purpose of removing alkali metal or the like affecting on the operation of the gas turbine and refining the gas to keep safeness of the environment and remove sulfur content for the prevention of corrosion to machineries of the system. In general, a temperature required for the refining unit is about 400.degree. to 500.degree. C. in a case of desulfurization-dry-process or about 100.degree. C. in a case of desulfurization-wet-process for performing the desulfurization in a reducing gas.
For this purpose, in the power generation system of the prior art, the gas of high temperature exhausted from the gasifier is circulated through various heat exchangers to once cool the gas to considerably low temperature for the desulfurization and then the temperature of the gas is again raised through the heat exchanging operation and burning operation for driving the turbine. Thereafter, the gas from the turbine is again lowered through the heat exchanging operation to release it into atmosphere, thus involving complicated processes with considerable radiation heat loss at respective units or components, resulting in the lowering of the thermal efficiency.